Tobacco smoke filters and method of making the same



Dec. 19, 1967 SHOJIRO FUKUI 4 TOBACCO SMOKE FILTERS AND METHOD OF MAKING THE SAME Fi led Aug. 30, 1963 FEED CRIMPED VISCOSE FIBERS O.3-4.0 DENIER FORMING T ow 40,000 40,000 DENIER OPENING TOW MIXING REFORMING TOW ADHESIVE POWDER TREATING DRYING SOLVENT FINISHED FILTER PRODUCT INVENTOR SHOJ l RO FUKUI i m A ar 6:0,

ATTORNEYJ United States Patent 3,359,148 TOBACCO SMOKE FILTERS AND METHOD OF MAKING THE SAME Shojiro Fukui, Hon-machi, Toyonaka, Japan, assignor to Kurashiki Rayon Company Limited, Kurashiki, Japan, a corporation of Japan Filed Aug. 30, 1963, Ser. No. 305,853 Claims priority, application Japan, Sept. 19, 1962, 37/ 40,349 4 Claims. (Cl. 156-180) The present invention relates to improvements in tobacco smoke filters having excellent adsorbing ability, and more particularly, to a method of making the material for such filters by adhesively bonding crimped rayon fibers without substantially interfering with the flow of tobacco smoke therethrough.

Tobacco smoke filters using acetate fibers have 'heretofore been broadly used, yet the capacity for filtering nicotine, tars and the like from tobacco smoke is not limited to acetate fibers but it is also possessed by natural, manmade and synthetic fibers. A principal reason for using acetate fibers for tobacco smoke filters is attributable to the fact that they have a thermoplastic nature, and after spraying a solvent for acetate fiber such as triacetine, for instance, the tow is subjected to heat treatment so as to swell and adhere the fibers at the locations Where solvent softened fibers are in contact, thereby providing tobacco smoke filters with a tolerable increase in pressure drop. Another process for manufacturing such filters involves contacting thermoplastic fibers such as polyethylene at high temperatures, yet in this case the fiber to be used in limited to thermoplastic fiber only and also the sectional form of the fiber is substantially circular and smooth so that the surface area of the fiber per unit weight is comparatively small and the fiber itself is not cheap.

The present invention is characterized in that the fibers in a tow of crimped viscose rayon fibers are united at a number of random positions in the tow by treatment wtih a suitable adhesive-solvent combination, thereby providing quite many points in the filter, thereby providing tobacco smoke filters which have excellent adsorption ability and less increase of pressure drop in passing smoke and moreover which can be produced at lower cost.

These tobacco smoke filters in accordance with the invention may be made by subjecting viscose rayon tow having 15-40 crimps per inch and 0.3 to 4.0 denier per filament in a bundle of approximately 40,000-70,000 total denier to an adhesive-solvent treatment such as (1) First with a solvent having ability of dissolving or swelling the adhesives, then the adhesive powder is applied,

(2) The adhesive powder is admixed with a liquid which is capable of dis-solving or swelling the adhesive powder and then applied to the tow,

(3) After the adhesive powder has been admixed through the tow, it is contacted with the solvent as a liquid spray or as a vapor.

After any one of the above processes is adopted the solvent is eliminated by a suitable method, thereby providing possibly many contact points between adjacent crimped fibers. When the solvent is used as vapor form as in condition 3, it may be supplied in conjunction with a heating medium.

The reason why the viscose fiber is particularly used as the base material of the filter according to the invention is due to the fact that the viscose fiber has quite many variations in section of the fiber so that the surface area for adsorption is large and has better adsorbing ability for nicotine, tar and the like substances compared with thermoplastic materials and also lower manufacturing cost than the other manmade fibers and moreover, the filament length, denier, number of crimps and shape of the fiber can be selected as desired.

The finer the monofilament denier, the greater is the surface area per unit weight of the fiber and the filtering effect on tobacco smoke likewise increases. Also, the spaces between fibers are finer so that the flow of the smoke therethrough is retarded with improvement in eliminating harmful substances in the smoke. Accordingly, in order to manufacture tobacco smoke filters having larger ability of eliminating harmful substances it is necessary that the monofilament denier should be less than 4 denier. On the other hand, when the monofilament denier is excessively thin (less than 0.3 denier) the spinning of such filament becomes difficult and the tenacity and elongation are reduced and also the opening of fibers after mechanically crimped becomes difiicult.

As above described, in order to make finer monofilament to provide tobacco smoke filters having excellent adsorbing ability it is necessary to select the total denier within 40,000 to 70,000. This is due to the fact that if the total denier of the tow is made more than 70,000 denier the number of filaments constituting the tow increases as the monofilarnent denier is reduced so that gaps between fibers allowing to pass tobacco smoke become smaller, thereby making the passing speed of smoke extremely slow and increasing the pressure drop when smoking the cigarette. On the other hand, if the total denier is less than 40,000 denier the number of filaments constituting a tow is so reduced as to lower the filtering ability below the practical value. The total denier of 40,000 to 70,000 denier according to the invention is much less than that of acetate rayon filters available at present on the market and has advantages that the weight of fiber used per filter tip can be reduced and the manufacturing cost is lowered.

With such fine monofilament and so small total denier for the fiber tow, the number of crimps per inch should be within the range of 15 to 40 which is much greater than the number of crimps of the acetate rayon filter at present on the market. That is, when the number of crimps is less than 15 per inch, the gaps between fibers tend to be larger thereby shortening the passage of the smoke through the filter and also it is impossible to maintain the rigidity and resilience desirable for tobacco filters. If the number of crimps is more than 40 per inch, the reduction in height of the crimps counteracts the benefit of the increased number of crimps the increase of number of crimps so that it is not desirable.

In carrying out the invention, monofilament denier, total denier of the fiber tow and the number of crimps have intimate relation to the filtering ability for smoke, desirable rigidity and resilience and increase in the pressure drop the molded filter possess. In general, when finer denier is used better results may be obtained by reducing the total denier and increasing the number f crimps. The most preferable condition within the above specified range is a monofilament denier of 1 to 2 denier, a total denier of 50,000 to 60,000 denier and number of crimps of 17 to 20.

The adhesive powders to be used in the invention are natural products such as starch, dextrin; and synthetic compositions such as cellulose derivatives such as cellulose acetate, cellulose propionate, methyl cellulose, ethyl cellulose, hydroxy methyl cellulose, carboxy methyl cellulose; vinyl resins such as polyvinyl alcohol, polyvinyl acetate, vinyl acetate copolymers, polyvinyl formal, polyvinyl chloride copolymer, polyvinyl pyrolidone, polystyrene; and acryl resins such as polyacrylic esters, polymethacrylic esters.

Among the above adhesives, water soluble or swelling adhesives can use water as the solvent so that the operation is not only simple but also the cost is quite low; and there is no danger of poisoning from the vapors. Adhesivesusing organic solvents have an advantage in that drying is simple and they have a high sticking strength which imparts desirable rigidity and resilience in the filter product. Considering from the point of cost of the adhesives and of solvent used in association with the adhesives, the rigidity, resilience, and increase in pressure drop of the molded filters, good results can be obtained by selecting, as water-soluble adhesive, polyvinyl alcohol and as adhesives soluble in organic solvents, polymethacrylate or cellulose esters. When the powder adhesive is applied, filters having uniform rigidity throughout the total sectional area can be obtained by uniformly distributing the adhesive over the fiber tow well spread by a suitable method. If, after the fiber tow is sufiiciently opened and the sectional shape is made about circular form, the adhesive powder is distributed from the periphery, then the powder is more concentrated along the periphery and less concentrated at the center and the filter having more rigidity on the outside and soft core can be obtained. On the contrary, if the adhesive is concentrated at the central part and less at the periphery there results higher pressure drop and difiiculty in molding so that it is impossible to provide preferable products. As the method of distributing adhesive powder to the fiber tow a conventional machine having construction like a conventional powder disperser may be used and also good result may be obtained by using electrodeposition apparatus.

In order to remove the solvent used in association with adhesive powders from the fiber tow various processes may be used such, for instance, as by wrapping the fiber tow applied with adhesive powders and solvents with paper and cut to a definite length and removing the solvent at about room temperature, or a method of removing in a drying machine under the reduced pressure or by heating, or a method of passing the paper wrapped fiber tow continuously through the drying machine, or passing the same tow wrapped with paper through a hot pipe.

Better results may be obtained'by comparatively finer grain of the adhesive powder, for instance, very good results may be obtained by usin powders more than 100 to 300 meshes and the powder of 50 to 100 meshes may also be used.

Whether the fiber tow isuniformly adhered or more rigid on the periphery and more loose at the center may be selected as desired according to the necessary condition of kinds of fibers to be used, swelling nature and solving ability of the solvent to the, fiber, adhesivity between fiber themselves, kinds of adhesives, method of applying adhesives, method of removing solvents, the filtering ability of tobacco smoke pressure drop, rigidity, resilience and cost of filters.

As the'method of adhering adhesives according to the invention concerns to the use of adhesive powders the rate of solvent to the adhesive can be selected smaller than that when concentrated adhesive solution is used and evenwhen the solvent swells the fiber the rate of reducing the swelling volume of fiber can be made small and the volume of the fiber tow is maintained constant so that there is no increase in pressure drop and the removal of solvent is easy 'as the quantity of solvent is small and the adhesion can be carried out effectively.

The nature of the invention will be more readily apparent from the accompanying drawing, the single figure of which is a flow sheet of the several steps and conditions for practicing applicants new and improved process for making tobacco smoke filters for cigarettes and the like. In the process as illustrated a tow of 40,000- 70,000 denier vicose fibers of 0.3-4.0 denier is opened, an adhesive powder is added to and mixed with the tow. After addition of the adhesive to the opened tow, the

tow is reformed and treated with a solvent for the adhesive whereby the adhesive is activated. Upon drying the fibers within the tow become joined at a plurality of points throughout the tow, thereby imparting the desired form and rigidity to the mass which can then be cut into filter plugs of a predetermined size.

Further details of the invention are also described in the following examples.

Example 1 Crimped viscose rayon tow (having number of crimps 15-16 per inch) 4 denier monofilament, 60,000 total denier of the fiber tow was thoroughly opened, then 15% of polyvinyl alcohol (average degree of polymerization' 1,700, saponification degree 88%) based on the weight of tow was uniformly dispersed by using a disperser and thus treated tow was wrapped with paper to 8 mm. dia. by using a cigarette making machine and cut to a length of 72 mm., then put in a sealed con tainer and subjected to steam treatment at 110 C. for 5 minutes and then taken out and cooled, then attached to one end of a cigarette according to a conventional process. The properties of the filter werecompared with an acetate rayon filter available at'present on the market and the results are shown in Table 1, wherein the pressure drop is shown by the hydraulic height when the air was passed at a speed of 20 m. lit/sec.

The removal,.rate of nicotine was measured by ultra violet absorption spectrum method and the rigidity was measured by the depth of a depression caused after 10 second pause after applying a load of 300 g. for 10 seconds to the filter plug and expressed by mm. unit.

Example 2 Crimped viscose rayon tow (number of crimps 18-20 per inch) of 1.5 denier monofilament and 50,000 total denier was thoroughly opened, then the tow was passed through a pipe of 10 mm. dia. to have substantially circular section and fine powder of cellulose acetate of about 10% of the weight of tow was'attached to the surface of the tow while rotating by using electric charge of an electro deposition apparatus from the periphery of the tow and wrapped with paperto 8 mm; dia. by using a cigarette making machine and cut to a length of 72 mm., then'put in a sealed container and after the air in the container has been removed it was treated with the vapor of methyl ethyl ketone at 110 C. for 5 minutes, then taken out of the container and cooled and left in air for 15 minutes and attached to one end of the cigarette by a known process. The properties of this filter was shown in Table 1.

Erample 3 Crimped viscose rayon tow (number of crimps 18-20 per inch) of 1.5 denier monofilament, 50,000 denier of total filament was thoroughly opened and powder of, methyl methacrylate of 7% of the weight of the tow was uniformly sprayed to the filament tow by using disperser, then glycerol triacetate solution of 10% of the weight of tow was sprayed, then the tow was wrapped with paper to 8 mm. dia. by using cigarette making machine and cut to a length of 72 mm. The 'filter thus formed was attached to one end of a cigarette by a conventional process. The properties of the filter are as shown in Table 1.

Example 4 Crimped viscose rayon tow .(number of crimps 2530 per inch) of 0.5 denier monofilament and 50,000 total denier was thoroughly opened and glycerol triacetate of 10% of the weight of the tow was sprayed, then after polymethyl methacrylate of 10% of the weight of tow was uniformly sprayed by a disperser and then passed through a pipe of 8 mm. dia. heated at C. to b dried, then the tow was wrapped with paper by using cigarette making machine and cut to a length of 72 mm. The filter thus prepared was attached to one end of a cigarette by a known process. The properties of the filter are as shown in Table 1.

TABLE 1 Conven- Property tional Ex.1 Ex.2 Ex.3 Ex. 4

Weight, g./12 mm 0.125 0.104 0. 090 0. 090 0. 094 Rigidity, 1/10rnm 4.8 4.2 4.6 4.3 4.9 Increase in pressure drop, mm. H2O 9s 83 75 7s 71 Removal rate of nicotines, percent. l 18 32 36 37 45 Removal rate of tars,

percent 20 35 37 37 42 It will be apparent from the Table 1 the filters of the invention is much superior in properties to those of known filters.

What I claim is:

1. A method for the manufacture of tobacco smoke filters which comprises in sequence the steps, (1) providing a tow of parallel crimped rayon fibers, said fibers having a monofilament denier of 0.3 to 4.0 and 15 to 40 crimps per inch, the total denier of said tow being 40,000 to 70,000, (2) opening said tow, (3) applying an adhesive in powder form to the fibers in said opened tow, (4) reforming the thus-treated tow, (5) thereafter applying to the tow a solvent for the said adhesive, and (6) evaporating said solvent from the tow whereby cri-mped fibers adhere within said tow.

2. The method according to claim 1 in which the adhesive is cellulose acetate and the solvent is methyl ethyl ketone.

3. The method according to claim 1 in which the adhesive is polyvinyl alcohol and the solvent is an aqueous fluid.

4. The method according to claim 1 in which the adhesive is methyl methacrylate and the solvent is glyceryl triacetate.

References Cited UNITED STATES PATENTS 2,794,759 6/1957 Dildilian 156-148 X 2,979,433 4/1961 MacHenry 156-180 X 3,026,226 3/1962 Touey et a1. 156-180 3,039,908 6/1962 Parmele 131-208 3,079,978 3/1963 Cobb et al. 156-441 2,483,406 10/1949 Francis 131-208 2,805,671 9/1957 Hackney et a1. 131-208 3,017,309 1/1962 Crawford et a1. 131-208 3,079,929 3/1963 Mueller 131-208 EARL M. BERGERT, Primury Examiner. MELVIN D. REIN, Examiner.

I. P. MELOCHE, Assistant Examiner. 

1. A METHOD FOR THE MANUFACTURE OF TOBACCO SMOKE FILTERS WHICH COMPRISES IN SEQUENCE THE STEPS, (1) PROVIDING A TOW OF PARALLEL CRIMPED RAYON FIBERS, SAID FIBERS HAVING A MONOFILAMENT DENIER OF 0.3 TO 4.0 AND 15 TO 40 CRIMPS PER INCH, THE TOTAL DENIER OF SAID TOW BEING 40,000 TO 70,000, (2) OPENING SAID TOW, (3) APPLYING AN ADHESIVE IN POWDER FORM TO THE FIBERS IN SAID OPENED TOW, (4) REFORMING THE THUS-TREATED TOW, (5) THEREAFTER APPLYING TO THE TOW A SOLVENT FOR THE SAID ADHESIVE, AND (6) EVAPORATING SAID SOLVENT FROM THE TOW WHEREBY CRIMPED FIBERS ADHERE WITHIN SAID TOW. 